1. Field of the Invention
The present invention relates to an antenna switching method of a wireless communication system for selecting one antenna, excellent in a communication quality state, from a plurality of antennas and being capable of performing transmission/reception. More specifically, the invention relates to the antenna switching method of a wireless communication system for accelerating establishment of a communication state, stably transmitting/receiving a signal, and reducing battery consumption.
2. Description of the Related Art
The applicant proposes a wireless communication system that incorporates a transmitting unit in a tightening torque measuring unit attached to a rotating shaft of a tightening machine or the like and is capable of wirelessly transmitting tightening information such as a torque value and a rotating angle to a receiving unit.
However, the tightening torque measuring unit has one antenna on a transmitting side, and this unit rotates integrally with the rotating shaft. For this reason, when the transmitting antenna moves to a position where a quality state of the communication with a receiving unit is deteriorated due to a position where the tightening torque measuring unit stops, transmission/reception of a signal to/from the receiving unit possibly fails.
It is considered that a plurality of transmitting antennas is successively switched and signals are successively transmitted (for example, see Japanese Unexamined Patent Publication No. 2000-353998). In this case, however, there arises the problem that the transmitting/receiving operation in a bad communication quality state is repeated at constant intervals.
Therefore, a method for arranging a plurality of transmitting antennas on a tightening torque measuring unit and transmitting tightening information from the transmitting antennas all together is considered. However, since the tightening torque measuring unit rotates integrally with the rotating shaft as described above, the unit should be driven by a battery as a power source. Hence, there arises the problem that increase in power consumption causes consumption of the battery to be sped up.
These problems are desired to be resolved not only in the torque measuring unit but also particularly in wireless communication systems required to sequentially transmit various signals.